Just to forestall a possible follow up question - yes, whirlwind and great cleave is subject to abuse:
Case 1 - you are surrounded by a demon and seven of his kobold buddies. You whirlwind attack, drop the first kobold, cleave onto the demon, attack and drop the second kobold, cleave onto the demon, attack and drop the third kobold, cleave onto the demon... etc. Finally you take your ordinary whirlwind attack against the demon. That makes eight full-attack-bonus attacks on the demon in one round. Wow
Case 2 - the evil troll charges towards you, surrounded by a double ring of kobolds within his 10 ft reach. He starts a whirlwind attack against all his pet kobolds, and with each hit he cleaves onto you. The total number of cleave attacks he gets on you will be left as an exercise for the reader
Case 2b - the PC with a spiked chain carries around a bunch of trained rats/dominated kobolds/whatever and uses the same tactic... i.e. engineer a situation where whirlwind attack against numerous weak targets enables multiple cleaves onto a single tough target.
The only thing that the current FAQ says on this issue that I can find is this:
Do the Whirlwind Attack and Cleave feats stack? For
example, can I use Cleave to get extra attacks if a
Whirlwind Attack kills one of my targets?
You can use Cleave only once a round. If you have the
Great Cleave feat, however, you can cleave each time you
drop an opponent, even when the opponent drops in a
Whirlwind Attack. (When a foe drops, resolve the extra
cleave attack before finishing the rest of the attack rolls in
the Whirlwind Attacks.)
So unfortunately the current FAQ legitimises this awful "multiple free attacks" rules loophole.
IMO it would make more sense to take the cleave (or great cleaves) after the entire Whirlwind sequence finishes - so if *any* of the targets is dropped, you can great cleave onto another target... and if you drop that one you can go on (etc). This is not what the FAQ says, but it would enable the abilities to work together well without the multiple free attacks syndrome.
Cheers